[CVE-2026-68479][MODERATE 7.0] Bluetooth: btrtl: validate firmware patch bounds

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-68479
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: btrtl: validate firmware patch bounds
Commit: 39e01b4addfbbe177567d6ed1dfb81f9cccb19e6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39e01b4addfbbe177567d6ed1dfb81f9cccb19e6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68479
Analysis date: Sun, 16 Aug 2026 04:41:33 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed Realtek Bluetooth firmware patch can trigger integer underflow in `rtlbt_parse_firmware()`, causing an oversized read and write during Bluetooth setup and creating a kernel memory corruption risk that is usually local firmware-controlled but should be manually reviewed.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68479 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68479

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68479	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-191;*CWE-787;CWE-125;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'rtlbt_parse_firmware() can process a malformed Realtek Bluetooth firmware patch with a patch_length smaller than the firmware version field. The subtraction used for the copy length can underflow and turn the copy into an oversized read and write during Bluetooth setup, and the old patch_offset plus patch_length range check can also wrap on 32-bit systems. This is a local firmware input attack rather than a Bluetooth over the air attack, because the attacker normally needs a way to place or influence the firmware blob loaded by the kernel. For the CVSS the PR:L is used in the paranoid score because some deployments may delegate firmware update or device setup control to a reduced capability service account or container context, while the normal host configuration is closer to PR:H. Impact is kernel memory corruption with at least denial of service and a plausible privilege escalation risk if a less privileged actor can control the firmware blob. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	OOB SIMPLEFIX HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The malformed input is a firmware patch blob, not normal Bluetooth radio traffic.
* Memory corruption, strong corruption primitive: +2. The patch fixes an integer underflow in `patch_length - 4` that can turn a copy into an oversized read and write.
* Reliable kernel crash / strong DoS: +1. Oversized copy during Bluetooth setup can plausibly crash the kernel.
* Privileged kernel/device-management memory corruption path: +1. The corruption happens in a trusted Bluetooth driver firmware parsing path.
* Integrity impact plausible: +1. An oversized write into kernel memory is an integrity-relevant primitive.
* Requires admin/root/CAP in typical deployments: -2. In normal systems, replacing firmware under `/lib/firmware` or equivalent is root-controlled.
* No attacker-controlled overwrite target / constrained exploitability: -1. The patch shows oversized copy, but not target selection, reclaim, callback control, or a demonstrated LPE primitive.

Paranoid additions / changes:

* Local lower-privilege trigger: +1. Some deployments may delegate firmware update, device setup, or containerized hardware-management paths to a reduced-privilege service.
* Privilege escalation plausible: +1. Kernel heap overwrite from attacker-influenced firmware is a credible LPE concern, but no reliable exploit primitive is demonstrated.
* Confidentiality impact plausible: +1. The oversized read side can potentially copy adjacent kernel memory, although no direct disclosure channel is proven.
* The full root privilege penalty is not applied in the paranoid interpretation because reduced-capability firmware management is a realistic deployment pattern.

## 3. Reachability analysis

This is not realistically Bluetooth-over-the-air reachable. The attacker normally needs the ability to place, replace, or otherwise influence the Realtek Bluetooth firmware patch blob consumed by `request_firmware()` during device setup.

In typical deployments this is root or administrator controlled, so the conservative interpretation is privileged local. In environments with delegated firmware update services, containerized device management, or reduced-capability service accounts that can influence firmware blobs, PR can reasonably drop to a lower-privileged local actor for triage purposes.

The path is hardware and driver dependent, requiring affected Realtek Bluetooth support and firmware loading. It is not a broad networking path, but it is a trusted kernel driver initialization path parsing external firmware data.

Call-site confidence: medium. The patch context clearly shows the vulnerable bounds check and the commit explains the oversized read/write consequence, but full allocation/copy call-site context is not included here.

## 4. Severity interpretation

This is more than an ordinary Moderate validation fix because the downstream primitive is explicitly an oversized read and write caused by integer underflow and overflow-prone range checking. Realistic exploitation is constrained by firmware control requirements, so the conservative score remains borderline.

The paranoid interpretation is Actionable Moderate to Strong Important candidate because attacker-influenced firmware parsing in kernel driver setup can create memory corruption, and reduced-privilege firmware management models can make the trigger more practical than full host-root only. Theoretical LPE is plausible, but not demonstrated by the patch alone.

## 5. One-sentence report phrase

A malformed Realtek Bluetooth firmware patch can trigger integer underflow in `rtlbt_parse_firmware()`, causing an oversized read and write during Bluetooth setup and creating a kernel memory corruption risk that is usually local firmware-controlled but should be manually reviewed.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes an integer underflow and overflow-safe bounds check around a firmware-controlled copy that can become an oversized kernel read/write. Even though normal reachability is privileged, the memory corruption class and possible delegated firmware-control scenarios make auto-closure unsafe.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: Bluetooth: btrtl: validate firmware patch bounds
Commit: 39e01b4addfbbe177567d6ed1dfb81f9cccb19e6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39e01b4addfbbe177567d6ed1dfb81f9cccb19e6

Commit description:

rtlbt_parse_firmware() copies patch_length - 4 bytes before appending the
firmware version. A malformed firmware patch shorter than the version field
can make this subtraction underflow and turn the copy into an oversized
read and write during Bluetooth setup.

The existing patch_offset + patch_length check can also wrap on 32-bit
architectures. Validate the patch length and range without arithmetic
overflow before allocating or copying the patch.

Fixes: db33c77 ("Bluetooth: btrtl: Create separate module for Realtek BT driver")
Cc: stable@vger.kernel.org
Signed-off-by: Laxman Acharya Padhya <acharyalaxman8848@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/bluetooth/btrtl.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39e01b4addfbbe177567d6ed1dfb81f9cccb19e6

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-68479 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68479

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 7

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).